This invention relates generally to gas turbine engines and more particularly, to engine control systems used with gas turbine engines that include prebooster and precompressor water injection, and variable inlet guide vanes.
Gas turbine engines typically include a compressor for compressing a working fluid, such as air. The compressed air is injected into a combustor which heats the fluid causing it to expand, and the expanded fluid is forced through a turbine. The compressor typically includes a plurality of compression stages sometimes contained in a separate low pressure compressor and a high pressure compressor.
The output of known gas turbine engines may be limited by signals received by the engine controller indicative of the speed of the rotor shafts, sometimes referred to as XN2 for the speed of the low pressure rotor, and XN25 for the speed of the high speed rotor, as well as the temperature of the working fluid at the output of the high pressure compressor, sometimes referred to as temperature “T3”, and by the temperature of the working fluid in the combustor outlet, sometimes referred to as temperature “T41”. The indication of the temperature at the outlet of the combustor T41 is recorded by temperature sensors at a downstream location, such as the outlet of the high pressure turbine, which is sometimes referred to as “T48”. To reduce both the T3 and T41 temperatures, while maintaining a constant flow of the working fluid, at least some known engines use an intercooler positioned in the fluid flow path between the low pressure compressor and the high pressure compressor. In steady state operation, the precooler or intercooler extracts heat from the air compressed in the compressor, which effectively reduces both the temperature and volume of air exiting the high pressure compressor. Such reduction in temperature reduces both the T3 and T41 temperatures. Increased power output therefore can be achieved by increasing flow through the compressor. However, such an intercooler may also reduce thermal efficiency of the engine.
To facilitate reducing both the T3 and T41 temperatures for power augmentation, without sacrificing engine thermal efficiency, at least some known engines include prebooster or precompressor water injection. The water spray facilitates reducing both the T3 and T41 temperatures, and also reduces compressive engine horsepower. Because the T3 and T41 temperatures are reduced, the engine is not T3 and T41 constrained, the engine may operate at higher output levels below the T3 and T41 temperature limits.
To facilitate optimizing power production from the gas turbine engine, at least some known engines that include water injection also employ variable inlet guide vane (VIGV) assemblies. The VIGV assemblies include a plurality of variably positioned inlet guide vanes that when rotated, facilitate changing the geometry of the gas turbine engines engine operation to facilitate improving engine performance over a wide range of engine operations. The combination of the water injection and the VIGV assemblies reduces an effective inlet flow temperature such that the gas turbine engine may be operated with increased power before being T3 and/or T41 temperature limited.